The invention relates to a pyrotechnic gas generator and a method of producing the gas generator.
Known gas generators comprise a gas-tight outer housing consisting of at least two parts, a first part of which being a receiving part for pyrotechnic material and a second part of which being a base part which is connected with the receiving part by welding so as to form the outer housing. In gas generators hitherto, generally the outer housing is produced from a sheet metal body which is closed by the base part, likewise of sheet metal. When the receiving part has a radially surrounding, i.e. circumferentially closed, flange for connection to the base part and the flange is welded to the base part, this usually takes place by simultaneous application of a pressure onto the radial flange, in order to press the latter against the base part. During welding, the flange is deformed by the heating and pressed in the radial outward direction so that the peripheral edge, i.e. the radial outer edge surface, of the radial flange is not arranged so as to be exactly defined relative to the base and often projects radially beyond the base, so that the base together with the peripheral edge subsequently have to undergo a metal-cutting process on their outer sides.
U.S. Pat. No. 4,402,269 discloses a detonator with an outer and an inner housing. The cup-shaped inner housing has a radial protruding flange arranged between radial flanges of two parts defining the outer housing. The three flanges are welded together at their radially facing outer edge surface. The welding defines the outest portion of the detonator which has a geometry and dimension which can, due to the welding process, not be predicted very precisely. Further, as three flanges are to be welded together the quality of the welding is to be extremely high, in order to achieve moisture and gas tightness.
An example of a non-welded gas generator comprising a base part and a sheet metal housing part is disclosed in German Laid-Open Document 34 25 836. The cup-shaped housing part has a surrounding flange with which it is inserted in a groove in the base part. The two parts are firmly connected with each other in that a surrounding lip on the base part is crimped inwardly towards the cup-shaped part. The flange has the purpose of forming a counterpart for the crimped portion which serves both for axial and radial positioning of the two parts.
The invention provides a pyrotechnic gas generator in which the subsequent working can be dispensed with and in which the peripheral edge of the flange has a defined, predeterminable position and dimension. This is achieved in a pyrotechnic gas generator which comprises a gas-tight outer housing consisting of at least two parts, a first part of which being a receiving part for pyrotechnic material and a second part of which being a base part which is connected with the receiving part by welding so as to close and to form the outer housing. One of the first and second parts has a radially projecting, surrounding, i.e. circumferentially closed, flange with an outer peripheral edge, i.e. an edge facing in the radial direction, and the other one of said first and second parts has an axially extending, rim-like projection circumferentially surrounding the peripheral edge and having a radial inner surface which is contacted by the peripheral edge. The welding of the first and second parts is provided at the flange at the axial surfaces lying on each other.
In the gas generator proposed, the flange can possibly be deformed slightly radially outwards during welding; however, it then abuts at the projection on the other part which delimits the deformation. Thus, a finishing step of the peripheral edge is no longer necessary, because the peripheral edge no longer protrudes radially with respect to the base. The new device can be used in large numbers reliably with regard to fail-safeness, and is suitable for a large-scale technical application. Also the reduction of test steps and hence costs is to be mentioned as an advantage.
Preferably the axial height of the projection corresponds to the axial thickness of the flange allowing the welding apparatus to easily reach and press the radial flange against the other part.
According to an embodiment, the outer housing completely consists of metal, e.g. by the receiving part being produced from aluminum. Furthermore, however, the invention can also be realized with an all plastic housing.
The welding takes place by capacitor discharge welding, a welding process in which usually the two parts are also pressed against each other during the application of the welding current, or ultrasonic welding.
As the receiving part is usually a thin-walled, cup-shaped, deformed part, it preferably has the radial flange which can be formed by simple deformation.
The gas generator according to the invention can be an igniter which is sealed hermetically to the exterior. The invention further relates to a gas generator in which the outer housing is provided to accommodate the propellant charge and the igniter. The igniter is positioned in the base part.
In the preferred embodiment, it is further considered that the propellant charge immediately adjoins the outer housing on the inner face.
The invention further relates to a method of producing the gas generator according to the invention.